Best materials I’ve seen for homemade are 10-12 oz (or more) denim. Women’s jeans rarely hit that nowadays. Two layers of that with a sandwiched layer of several passes of chiffon or silk. Flannel is also somewhat effective. Theory is that the thick weave of the denim is more of a mechanical filter to catch the water droplets and the silk or chiffon are an electrostatic layer that will catch smaller particles. That said, almost all of the most effective materials are non-woven, so...
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As for other inner filters.... Do not under any circumstances use HEPA filters (also many or most vacuum cleaner bags). They all contain fiberglass. Some sites say don’t use furnace filters. I say do your research. Don’t look for reason you can use them, find reasons you can’t and see if you can disprove those. Some brands have lines that are acceptable. Other brands have none. Other brands are entirely ok.
Just make sure it fits tight, is washable, covers the entirety of your nose up to the middle of the bridge and down below your chin. Secondary concern is comfort. If it’s not comfortable, you’ll be less likely to use it. Ear savers are a godsend. Being able to secure the mask behind your head and neck as opposed to using your ears is preferable. Stay clean shaven, always.
Any gaps, even small ones, will reduce effectiveness dramatically. Make sure you have a means of donning and doffing without touching the mask material, just the ties. Consider buying or making a mask with a copper wire (or some other sort of malleable metal) that can be used as an adjustable nose clip to ensure it doesn’t fall down AND to make sure it has a tight seal. I’ve also heard ideas like running a bead of silicone around the edges can help make a more effective seal on homemade ones. Ymmv.
If you think you’ve been exposed to someone, wash your hands very well, remove the mask carefully, wash your hands very well again, don a new mask. Which is another good point, have several. Like at least two or three.
If you have surgical masks or respirators, you can wear one, put it in a clean paper bag, and isolate it for five (CDC) to ten (world’s foremost respirator manufacturer) days depending on who you believe. UV, ozone, water, alcohol etc. may degrade your rated mask. I’m not a big fan of disinfecting when time will also do the same, perhaps more effectively, without degrading the materials.
And in the end, the masks aren’t for you, they’re for us. So don’t be a ****ing dick; wear a mask even if it’s a cut up white kitchen towel.
